Robert Bellah's book is dense with theories and examples. To pull out any particular theme risks distortion. Nonetheless, it's clear that one of the big stories of his book is an account of how religions have changed from being only a way to express or to discover their societies to becoming, potentially, a way in which to criticise them. Since, as he often says, nothing is ever lost, those religions that acquired an idea of utopia, or of absolute moralities, did not thereby abandon their older uses. Religions became divided within themselves as part of the process by which they made it possible to criticise existing societies. That's yet another reason why generalisations about "religion" will always find counter-examples, even when they are confined to modern and literate religions.

One such generalisation is that religions entail worship. This isn't true of the rituals and mythologies we have so far studied, and Bellah dates the emergence of gods, who require worship, to a particular set of economic and social changes. This kind of god is "not so radically different from the powerful beings we have already encountered, but … their relation to humans as exemplified in their role in ritual has shifted: they are now worshipped."

Worship involves submission rather than invocation. The worshippers kneel or prostrate themselves. They offer gifts. This isn't just a recognition of God's higher status – it's also a hope that some of this status will rub off on the worshipper. This is a subtle but important difference from the kind of relationship implied in ritual.

In the kinds of hunter-gatherer ritual discussed last week, where the spirit world is understood as the domain of "powerful beings", the relationship is closer to possession by humans: "Powerful beings among the Kalapalo, Australian Aborigines and Navajo were often, though not always, alpha male figures, who could be terribly destructive when crossed, even inadvertently, but with whom people could identify if they followed the proper ritual, and, through identification, their power could become, at least temporarily, benign."

But when the gods are conceptualised as powerful chiefs – more like the Homeric gods than the Navajo powerful beings – they fit into the hierarchy of power that descends through earthly societies, too. Worship becomes something that can only effectively be performed by the right people. Something like a priesthood emerges, though the priests are also chieftains.

Bellah takes his examples for this part of the story mostly from Polynesia. The process must have gone on among almost all human societies, but in Polynesia it was still happening according to its own logic when literate westerners turned up to observe and record it. The islands were almost entirely isolated from the states that emerged in China and some parts of America, so their development is in a sense purer than that of any surviving hunter-gatherers, almost all of whom now are remnant populations driven out to the margins of the world.

Priests and kings both live off a surplus. There must be a surplus – at least of food – which can be redistributed, and redistribution implies inequality. Even in societies built around the generosity of chieftains, there is always an imbalance of power between those who give and those who receive. Generosity can be a mark of condescension.

On Polynesian islands, where there was both a possibility of surplus and a clear limit to the resources of any society, Bellah traces the simultaneous rise of organised religion and organised warfare. On Easter Island, the evidence of both is everywhere: the great carved heads looking down on the shattered remains of the society that built them, which destroyed itself and its ecology in unremitting centuries of internecine war.

In Hawaii, just before the Europeans arrived, society seems to have carried these tendencies towards another extreme.

"A stark distinction between social classes, even the existence of an outcaste class; heavy taxation of commoners; land expropriation at the will of chiefs; and – perhaps symbolic of the kind of society Hawaii had become – frequent human sacrifice. Chiefs ruled by divine right but also by force; and they could be conquered and killed by force."

What's important for his larger argument is that these developments were all new. There had been religions before without them. There have been religions since without them. But the kinds of religion that emerged in Hawaii, among many other places, correspond very well to the Voltairean model of all religion – a fraud in the service of despotism and inequality. Voltaire himself was cynical – or enough of a realist – to want to benefit from this. He wanted his servants to believe, because it kept them honest. Perhaps it is in the nature of all stable social systems to be able to buy off their most dangerous critics. But the Voltairean critique ignores the most interesting question, which is how some religions developed beyond institutionalised power worship. This is, for Bellah, the central question of the axial age, where his book ends. When gods first appear as the gigantic shadows of earthly tyrants, what is it that changes, and how, to make God instead into a source of light in which we can judge all societies, and even ourselves, against an ideal of justice?